Device for writing and/or reading optical recording medium of various designs

ABSTRACT

A device for writing to and/or reading from optical recording media having different structures is described, for example, a device which is suitable both for writing to/reading from digital videodisks (DVD) and conventional CD&#39;s. Provision is made for measuring the intensity of each peak in the mirror signal while the objective lens is moving to the recording medium. The intensity e.g. at the instant of the positive-negative crossing of the focus error signal is taken in this case. The type of optical recording medium is determined from the time characteristic and/or the height distribution of the peaks. In order to identify the type of optical recording medium, different properties of the optical recording medium are taken into account, such as reflectivity of the corresponding reflective surface, reduced intensity modulation due to spherical aberration, time characteristic and the like.

The present invention relates to a device for writing to and/or readingfrom optical recording media having different structures.

A device of this type is disclosed, for example, in EP 0 294 490 or “IBMTechnical Disclosure Bulletin, Vol. 29, No. 3, August 1986”. In thesedevices, the type of optical recording medium is determined using thereflectivity of the recording layer. In this case, the intensity of thereflected light is compared with two reference values, which permit adistinction (discrimination) between two types of recording media.

In the device disclosed in “IBM Technical Disclosure Bulletin, Vol. 29,No. 3, August 1986”, the reflectivity of the optical recording medium isused to determine the type thereof. The objective lens of the device isin this case moved from a reset position towards the recording medium.The signal emitted by a focus detector during this process is used todetermine the type of optical recording medium. Only those regions ofthe signal characteristic which lie above a first reference value (LOW)are used here. If the magnitude of the signal lies above the firstreference value but below a second, higher reference value (HIGH), thenan AND gate emits a pulse which signals that a “write-once” recordingmedium has been inserted. If the magnitude of the signal lies both abovethe first reference value and above the second, higher reference value(HIGH), then a further AND gate emits a pulse which signals that a“read-only” recording medium has been inserted. This method functionswhenever the recording media used can be identified unambiguously usingthe reference values. A relatively large number of different types ofoptical recording media makes it necessary to introduce, if appropriate,additional reference values, which are inevitably closer together, as aresult of which the error probability rises. If a plurality of extremevalues lying between the lowest and the highest reference value appearin the signal characteristic, then the result in this method may be thata plurality of contradictory statements relating to a single recordingmedium are output concerning its type, which may result in the devicemalfunctioning.

EP 0 294 490 discloses, for the purpose of determining the type ofoptical recording medium, evaluating the signal level of the RF signal,that is to say of the signal carrying the information read from therecording medium. In this case, provision is made for evaluating thesignal level whenever the objective lens is in a position suitable forreading, that is to say its focus point lies on or almost on thereflecting layer of the recording medium. As long as the type of opticalrecording medium is still unknown, the device cannot be set optimally,that is to say the RF signal is subjected to a greater or lesser extentto interference, with the result that the signal level can actually beevaluated only during a very brief time interval. Depending on the levelof the randomly read signal, it is possible in this case for largefluctuations to occur, with the result that it is necessary to take alarge error bandwidth into account, that is to say in this case, too,the problem arises that with a wide variety of different types ofoptical recording media having different thicknesses and/or numbers oflayers which is to be expected in the future, the signal levels used forthe discrimination are so close together that unambiguous discriminationrequires ever greater complexity or even becomes impossible. Moreover,unambiguous discrimination may be rendered virtually impossible byproduction-dictated slight fluctuations in the reflectivity of theoptical recording medium.

It must therefore be regarded as disadvantageous with these knowndevices that the wide variety of different types of optical recordingmedia having different thicknesses and/or numbers of layers which is tobe expected in the future can no longer be identified reliably by meansof a simple reference value analysis according to the prior art.

Devices suitable for reading from and/or writing to different types ofoptical recording media, in particular, should be capable of identifyingthe type of optical recording medium in order to be able correctly toselect parameters for the reading and/or writing operation.

The object of the present invention, therefore, is to propose a devicehaving a simple structure and an appropriate method by means of whichdifferent types of optical recording media can be identified reliablyyet rapidly.

This object is advantageously achieved by means of the measuresspecified in the independent claims. Advantageous developments of theinvention are evinced in the subclaims. In order to achieve the object,the invention provides an identification means which makes it possibleto determine the type of optical recording medium by assessing thephysical properties thereof. This has the advantage that the scanning orrecording properties of the device, which differ for different types ofoptical recording media, are automatically set in a manner correspondingto the determined type of recording medium.

According to the invention, the identification means is capable ofdetermining the layer thickness of the protective layer which covers therecording layer of the recording medium. This has the advantage that itis thereby possible to use recording media having different layerthicknesses as well in the device according to the invention. Futurerecording media of high storage density will have smaller layerthicknesses than conventional recording media, for example than CDs.

According to the invention, provision is made for carrying out, duringthe focusing operation of the device according to the invention, aplausibility check of the signals determined from the reflected light. Aplausibility check of this type has the advantage of managingessentially without any additional hardware elements, since it ispossible to utilize functions and components which are present in anycase. This plausibility check may consist, for example, in implementingdifferent scanning or recording properties, suitable for different typesof recording media, of the device with corresponding focus settings.Since the respectively set values are coordinated with different typesof optical recording media, that is to say with optical recording mediahaving different physical properties, the signals emitted by thedetection means lie in a meaningful range of values only when thesetting of the device is matched to the type of recording mediuminserted. The type of optical recording media involved can be derivedfrom that setting for which these signals are the most plausible.

A further aspect of the present invention provides for evaluating aplurality of characteristic features in the time characteristic of theintensity of the light reflected from the optical recording medium, forthe purpose of determining the physical properties and hence the type ofthe optical recording medium. This measure is based on the insight thatthe time characteristic of the intensity depends on the type of opticalrecording medium. In this case, the time characteristic also includesreflections at the air-substrate material transition layer or at thetransition layers of different layers of the optical recording medium,with the result that a relatively large number of information items areavailable for the evaluation. The time characteristic of the intensityof the reflected light differs, for example, for optical recording mediahaving different thicknesses. Optical recording media which can beprerecorded or are prerecorded on both sides have, for each side, onlyabout half the thickness of a conventional optical recording medium, forexample of an audio CD. A distinction can likewise easily be madebetween different optical properties, for example different refractiveindices of the substrate material of the optical recording medium anddifferent reflectivities of the optical recording layers used,particularly when two or more layers of recording layers are arrangedone above the other. In contrast to the prior art, in which a recordingmedium provided with two recording layers is determined only using thelayer having the highest reflectivity, which can easily lead toincorrect assignment, such errors are virtually precluded with thedevice according to the invention. The light reflected from the opticalrecording medium is in this case detected by detection means. In thesimplest case, the detection means consist of a photodetector, whichemits an electrical signal proportional to the intensity of the lightincident on it. In an advantageous development, the detection means areassigned a processing stage, in which the signal of the photodetector isprocessed and/or conditioned.

According to the invention, the signals emitted during the displacementof the focus point along the optical axis are evaluated. This has theadvantage that it constitutes a simple measure which does not requireany additional circuitry and time, since the focus point must in anycase be moved towards the optical recording medium in order to find itscorrect position with reference to the recording medium.

According to the invention, the time intervals between the extremevalues of the emitted signals are determined. This has the advantagethat in this way the layer thickness or the distance between a pluralityof layers that are present can be determined in a simple manner. Evengreater accuracy of the assignment of the type of optical recordingmedium can be achieved if the magnitude of the extreme values of theemitted signals is additionally evaluated. In this case, it is possiblejust to determine the sequence and the magnitude of the extreme valuesor else additionally to take account of the time interval. The magnitudeof the extreme values, which may be both maxima and minima, correspondsto the reflectivity of the corresponding recording layer. A comparisonof the relative or else of the absolute magnitudes of the extreme valuespermits reliable identification of the different types of opticalrecording media.

Furthermore, the invention manifests the possibility of comparing thetime characteristic of the intensity of the reflected signal with storedsignal characteristics which are characteristic of the different typesof optical recording media. Each of the stored characteristic signalcharacteristics is assigned the corresponding type of optical recordingmedium, with the result that the type of recording medium is determinedusing this comparison. In this case, the comparison is effected eitherdirectly or by means of a suitable mathematical algorithm.

In an advantageous development of the invention, the focusing means hasa multiple-focus lens, in particular a dual-focus lens, as is providedfor protective layers which have different thicknesses and cover theoptical recording layer. This yields a relatively large number ofextreme values in the time characteristic of the reflected signal. Thishas the advantage of enabling even more precise differentiation of thissignal. The said dual-focus lenses have two different focal lengths orcan be set to two different focal lengths, in order to be opticallymatched to two layers having different thicknesses. Optical matching tomore than two different layers is achieved by a correspondingmultiple-focus lens. It lies within the scope of the invention to useother suitable optical elements instead of a lens, which elements arecapable of producing a plurality of focus points, such as holographicoptical elements or polarizers, for example.

In order to identify the physical properties and hence the type of theoptical recording medium, it is likewise possible to provide a switch,which can be actuated by the operator. This has the advantage that thismeasure which is particularly simple to realize is cost-effective torealize. The switch may be, for example, a mechanical switch, atouch-sensitive key, a contactless sensor or the like. A measure whichenhances the operational convenience may be seen in the provision of acorresponding switch which is actuated by the optical recording mediumor a cartridge connected thereto.

The settings of the devices according to the invention areadvantageously altered by means of the method specified in the methodclaim, in order to be matched optimally to the type of recording medium.

The invention is described below using exemplary embodiments withreference to the figures. Advantageous developments of the invention canbe found in the description.

In the figures:

FIG. 1 shows a schematic sketch of a device according to the invention,

FIG. 2 shows a diagrammatic illustration of the determination of thetype of optical recording medium by means of a dual-focus lens using aconventional CD,

FIG. 3 shows a diagrammatic illustration of the determination of thetype of optical recording medium by means of a dual-focus lens using anoptical recording medium which is prerecorded or can be prerecorded onboth sides, has a high storage density and has a single recording layer,and

FIG. 4 shows a diagrammatic illustration of the determination of thetype of optical recording medium by means of a dual-focus lens using anoptical recording medium which is prerecorded or can be prerecorded onboth sides, has a high storage density and has two recording layers.

According to the schematic sketch, illustrated in FIG. 1, of areproduction and/or recording device for optical recording media AT ofvarying storage density, a scanning device which, in accordance withFIG. 1, consists of a laser diode LD, a grating G, a polarization beamsplitter PBS, a collimator lens CL, a quarter-wave plate WL, anobjective lens OL, a concave lens KL, a cylindrical lens ZL and adetector PD is used in a reproduction and/or recording device which isprovided both for playing back audio CDs and for playing back digitalvideodisks. Although the digital videodisks, called DVD below, and anaudio disk, called CD below, have a different storage density, thescanning unit illustrated in FIG. 1 can be used equally for both typesof recording media AT. The higher storage density of a DVD is achievedby a smaller pit size and a reduced track spacing in comparison with theCD. In order to reproduce the information stored on a recording mediumAT or record corresponding information, it is necessary to adapt thediameter of the scanning beam or writing beam, respectively, to the sizeof the storage elements or pits, respectively, that are used. In orderthat both the smaller pits of a DVD and the larger pits of a CD can beread using the scanning device indicated in FIG. 1, the objective lensOL is designed as a dual-focus lens. The dual-focus lens or else amultiple-focus lens can be used to realize different light spotdiameters on the information medium AT. This detector arrangement isadvantageously used both for recording media AT of high storage densityand of low storage density.

Output signals of the detection means PD are forwarded both forevaluation to known evaluation and regulating devices (not illustratedhere) and to the evaluation unit AE, which can receive additionalinformation from assemblies which are likewise not illustrated here. Anoutput signal of the evaluation unit AE is forwarded to a control unitSE, which controls a focus drive EA as a function of signals fromfurther assemblies (not illustrated here) such as a regulating device,for example. The said focus drive is part of the focusing means FM and,in the exemplary embodiment, serves to shift the objective lens OL alongthe optical axis OA. In the more general case, the focus point isshifted along the optical axis OA. The recording medium AT isillustrated with two different layer thicknesses d1 and d2. The layerthickness d2, which is illustrated on the right of the optical axis OA,corresponds to that of a conventional CD. The recording mediumillustrated as an alternative on the left-hand side of the optical axisOA has two layers having the thickness d1. This is an example of adigital videodisk DVD which can be prerecorded or is prerecorded on bothsides. The two focus points F1 and F2 and the objective lens OL, whichis in this case designed as a dual-focus lens, are furthermore evident.The layer thickness d1, d2 is, as illustrated here using the example ofthe CD and the DVD, an indicator of the type of optical recordingmedium.

The illustrated device for playing back from and/or recording on theoptical recording medium AT is capable of distinguishing between thedifferent types of optical recording media such as CD and DVD, forexample, in order that the control unit SE can drive the focus drive FAwith control signals matched to the corresponding type of recordingmedium AT.

In the simplest exemplary embodiment, a sensor or mechanical switch SW,which can be actuated by the user of the device and is illustrated bydashed lines in FIG. 1, or a sensor S, which detects the type ofrecording medium AT and is likewise illustrated by dashed lines, isarranged here instead of the evaluation unit AE.

If mechanical switches are dispensed with, then it is necessary togenerate in another way a signal by means of which the physicalproperties of the optical recording medium AT which is to be read fromand/or written to can be identified, in order that the control unit SEcan be set correspondingly.

This problem arises when the intention is to read from or write toconventional CDs in a device for reading from and/or writing to digitalvideodisks DVD. In order to manage with a read-out unit having arelatively simple structure despite the layer thickness differences d1,d2 of the different types of optical recording media, a dual-focus lensOL is used. In this case, each of the two focus points F1, F2 results ina light signal reflected from the recording medium. Only one of the twosignals contains the stored information. Since the track width isdifferent in a DVD and a CD, it is also necessary to match the trackingregulating circuit to the type of optical recording medium.

The optical recording media which are to be read from and/or written tomay have height or distance deviations from the focusing means FM of upto several millimetres, whereas the focus point F1 or F2 is permitted tomove away only by a few micrometres with regard to the recording layerAZS situated at the distance d1 or d2, respectively, from the undersideof the optical recording medium AT. To this end, in the exemplaryembodiment use is made of an automatic focusing system which regulatesthe distance between the objective lens OL and the recording layer AZSwith the aid of the focus drive FA. The signals for controlling thefocus drive FA are derived from signals emitted by the photodetector PD,that is to say parallel to the read-out of the information. Theso-called astigmatism method can be used, for example, for focusing.

After the insertion of an optical recording medium into the device, thecontrol unit SE first of all brings the distance between the objectivelens OL and the recording medium AT into a position in which the focuspoint is situated on or in the vicinity of the recording layer AZS ofthe optical recording medium, with the result that the automaticregulating circuit, whose regulating range is limited, can be switchedon. The operating range of the focus regulation is normally within therange from 10 to 100 micrometres, depending on the focusing method used.

In an initialization phase following the insertion of the opticalrecording medium AT into the device, the objective lens OL is usuallymoved at low speed in the direction of the recording medium AT. In asystem having a conventional lens, that is to say a single focal pointand, consequently, a single focus point, a narrow, pulse-like signaloccurs when the focus point of the objective lens OL moves into therecording medium AT, and a further, significantly larger pulse occurswhen the focus point, F2 impinges on the recording layer AZS. As long asthe focus point is not situated in the vicinity either of the surface orof the recording layer AZS, virtually no reflected light falls onto thedetector PD. If the focus point is situated just below a reflectivesurface, then a positive focus error signal FE is generated, forexample, from the signals emitted by the detector PD, whereas thissignal is negative as soon as the focus point is situated above thereflective surface. The value of the focus error signal FE is zero whenthe focus point is situated in a position suitable for writing orreading. The focus regulating circuit is usually switched on as soon asthe focus error signal FE=0.

If, as illustrated in the exemplary embodiment, a dual-focus lens OL isused, then the number of pulses measured by the detector unit duringinitialization is doubled. Two pulses occur each time the focus pointsF1 and F2 pass through the air-recording medium interface and therecording layer AZS. This case is illustrated in FIG. 2 using aconventional CD.

The top part of FIG. 2 illustrates a detail of a recording medium AT, inthis case a CD, which has been rotated through 90° in comparison withFIG. 1. The recording layer AZS is situated on the right-hand side, andthe recorded information is illustrated by the elevations anddepressions in the recording layer AZS. The bottom part of FIG. 2illustrates the time axis t and the voltage RV which is output by thecontrol unit SE to the focus drive FA during the initialization phasewhich has already been described above. The rising voltage RV causes theobjective lens OL to move towards the recording medium AT. The signalsemitted by the detector unit PD are likewise illustrated as focus errorsignal FE and as mirror signal M. The mirror signal M in this casecorresponds to the mean intensity of the light reflected from theoptical recording medium. This can be, for example, the envelope of theinformation signal.

For the exemplary embodiment, it is assumed that the dual-focus lens isdesigned in such a way that the intensity which can be measured at thefocus point F2 is about half as high as that which can be measured atthe focus point F1, which is provided for the read-out of the digitalvideodisk DVD. That part of the dual-focus lens OL which produces thefocus point F2 is spherically corrected to a layer thickness of therecording medium AT of d2=1.2 mm, whereas that part of the dual-focuslens OL which produces the focus point F1 is corrected to a layerthickness of d1=0.6 mm, corresponding to the layer thicknesses of CD andDVD, respectively. As illustrated in FIG. 2, four pulses, also referredto below as peaks, occur for a CD while the objective lens OL is beingmoved towards the recording medium. In this case, the peaks of themirror signal M are greatest when the focus error signal FE passesthrough a zero crossing directed from the positive to the negativerange. The first peak occurs when the CD focus point F2 passes thesurface of the recording medium. The intensity of the light reflectedhere is low, since the reflectivity of the surface is low, usuallyapproximately 4%, and the focus point has large aberrations. The mirrorsignal M is therefore small. The second peak occurs when the DVD focuspoint F1 passes the substrate surface. In this case, too, the intensityof the reflected light and, therefore, also the peak in the mirrorsignal are low. To be precise, on account of the low reflectivity of thesurface, on the one hand, and, on the other hand, on account of the factthat the spherical aberration for the focus point F2 is even higher thanfor the focus point F1, which is due to the higher numerical aperture.The third peak occurs when the CD focus point F2 reaches the recordinglayer AZS. The intensity of the light reflected here is high, since boththe reflectivity of the recording layer AZS is very high, usually atleast 70% for conventional CDs, and, on the other hand, only smallaberrations occur. The corresponding peak is therefore likewise high.The fourth peak occurs when the DVD focus F1 impinges on the recordinglayer. Although the intensity of the light focused at the focus point F1is about twice as high as that of the light focused at the focus pointF2, in accordance with the assumption for this exemplary embodiment, theintensity of the light reflected here is about as high as that at thefocus point F1, on account of the high aberrations.

FIG. 3 illustrates a diagrammatic sectional view as well as thecorresponding signal characteristics for a digital videodisk DVD havinghalf the layer thickness d1. Four peaks occur in the mirror signal M inthis case, too. The first peak occurs when the CD focus point F2 passesthe surface of the recording medium. It is small on account of the lowreflectivity and the large aberration. The same is correspondingly truefor the second peak, which occurs when the focus point F1 passes thesubstrate surface. The third peak is produced when the focus point F2impinges on the recording layer. The intensity of this peak is greaterthan those of the first two peaks, but is nevertheless relatively low onaccount of high aberrations of that part of the dual-focus lens OL whichis corrected to a layer thickness d2 and produces the focus F2. Thefourth peak occurs when the focus point F1 impinges on the recordinglayer. Since that part of the dual-focus lens OL which produces thisfocus point is corrected to the layer thickness d1 and double theintensity occurs at the focus point F1 when compared with the focuspoint F2, the fourth peak is about twice as high as the third peak.

FIG. 4 shows the signal characteristics and a sectional view for adigital videodisk having two recording layers AZS lying one over theother. The first two peaks in the mirror signal M correspond to thosedescribed with regard to FIG. 2 and to FIG. 3. The third peak occurswhen the CD focus point F2 impinges on one or on the two recordinglayers. The peak in the mirror signal is greater here than the firstpeaks, but is nevertheless relatively small on account of highaberrations. If these aberrations are small enough, that is to say ifthe entire optical system, in particular the dual-focus lens OL, iscorrespondingly well corrected, it is possible to distinguish betweentwo peaks. In the general case, however, these peaks will be superposedon one another in such a way that it is only possible to discern awidened peak, as illustrated in FIG. 4. When the DVD focus point F1impinges on the first recording layer AZS1, the fourth peak is producedin the mirror signal M. Since the dual-focus lens OL has the smallestaberrations for the focus point F1 in combination with the substratethickness d1 and double the intensity occurs at the focus point F1 whencompared with the focus point F2, but the reflectivity of the firstrecording layer AZS1 is only in the region of 30%, the intensity of thelight reflected here, and hence the height of this peak, isapproximately as high as that of the third peak. An additional, fifthpeak in the mirror signal occurs when the focus point F1 impinges on thesecond recording layer AZS2. The intensity of this peak is approximatelyof the order of magnitude of the preceding intensity. Although thefourth and the fifth peak are superposed on one another, they cannevertheless be discerned separately in the mirror signal. Thedistinction is made even more clearly in the focus error signal FE.

According to the invention, provision is made for measuring theintensity of each peak in the mirror signal M while the objective lensOL is moving up to the recording medium AT. The intensity at the instantof the positive-negative crossing of the focus error signal FE is takenin this case. The type of optical recording medium is determined fromthe time characteristic and/or the height distribution of the peaks. Thedecision-making process takes account of different properties of theoptical recording medium, such as reflectivity of the correspondingreflective surface, reduced intensity modulation due to sphericalaberration, time characteristic and the like.

In an idealized way of considering the exemplary embodiment, the speedof the objective lens OL can be determined from the time differencebetween the first two peaks and the known distance between the focuspoints F1 and F2. The layer thickness d1 or d2 can be inferred from thespeed information and the time which elapses between the occurrence ofthe second and of the third peak, since this time is proportional to thethickness d1 or d2 divided by the difference between the two focuspoints (d2−d1). In this way, it is possible to determine the layerthickness d1 or d2 and thus the type of optical recording medium CD orDVD, respectively.

If the intensity distribution of the third and fourth or of the third tofifth peaks is used, then a conventional CD is concerned if theintensity difference between the third and the fourth peak is relativelysmall. If the fourth peak is substantially greater than the third peak,then a DVD having a single recording layer AZS is concerned. If thefourth peak is split into a fourth and fifth peak, then a DVD having tworecording layers AZS1 and AZS2 is concerned. In this case, the thirdpeak, too, may already be split. Multiple splitting of the third orfourth peak indicates a digital videodisk having a plurality ofrecording layers AZS1 to AZSn, where n corresponds both to the number ofrecording layers and to the number of splittings.

A further possible way of determining the type of optical recordingmedium is to store the signal characteristic, for example the timecharacteristic of the mirror signal M or of the focus error signal FE,for each possible type of recording medium in a memory unit SP. Thestored signal characteristics are then compared with the currentlymeasured signal characteristic in a comparison device VE, and the typeof the actually inserted optical recording medium is determined on thebasis of this comparison. In this case, it is possible to use a widevariety of mathematical methods to bring the time scale of the measuredand of the stored curves into correspondence and to determine thelargest possible correspondence between the curves. Fouriertransformation and/or the convolution integral method can be used, forexample, to determine a maximum.

The individual devices advantageously operate in the manner describedbelow. To match the settings of a device for writing to and/or readingfrom an optical recording medium AT to the type of an optical recordingmedium AT, the following procedure is effected:

The focus point F1, F2 is shifted along an optical axis OA in accordancewith device settings which are suitable for a first type of recordingmedium, the light reflected from the optical recording medium AT duringthis operation is detected and a signal which corresponds to theintensity of the reflected light is generated, a check is made to seewhether this signal lies in a plausible value range and, if appropriate,the preceding step is repeated with settings which are suitable for afurther type of recording medium; the settings which are suitable forthat type of optical recording medium AT for which the signal lies in orthe nearest to a plausible value range are then selected and thesettings of the device are correspondingly matched.

Another method for matching the settings of a device for writing toand/or reading from an optical recording medium AT to the type of anoptical recording medium AT comprises the following steps:

Shifting of a focus point F1, F2 along an optical axis OA and detectionof the light reflected from the optical recording medium AT during thisoperation, determination of the type of optical recording medium ATusing characteristic features in the time characteristic of thereflected light, and setting of the parameters of the device to valueswhich are suitable for the determined type of optical recording mediumAT. In this case, the differences between the extreme values of the timecharacteristic of the reflected light are determined for the purpose ofdetermining the type of optical recording medium AT. Furthermore, inorder to determine the type of optical recording medium AT, there isprovision for comparing the relative and/or absolute values of theextreme values of the time characteristic of the reflected light withone another, or for comparing the time characteristic of the reflectedlight with stored reference time characteristics.

There is furthermore provision for using the MIRROR signal (M) or thefocus error signal (FE) and/or a focusing means FM having differentfocus points F1, F2 for determining the time characteristic of thereflected light.

What is claimed is:
 1. In a device for writing to or reading fromdifferent optical recording media, means for determining the type ofoptical recording medium in said device, said means comprising: anidentification means which determines the layer thickness of saidoptical recording medium by determining the distance between two regionsfrom a signal generated from reflected light; and an objective lensbeing moved to the recording medium at a constant speed; wherein saididentification means determines said constant speed of said objectivelens from a signal generated from said reflected light at said recordingmedium.
 2. A device for writing to or reading from different opticalrecording media, comprising: focusing means for shifting a focus pointalong an optical axis; detection means for detecting light reflectedfrom an optical recording medium; evaluation means for distinguishingthe type of optical recording medium by evaluating signals emitted bysaid detection means; and a control unit for controlling said focusingmeans; wherein said evaluation means includes a plausibility checkingunit, which checks said signals emitted by said detection means todetermine if said signals are within a predetermined range, and whereinsaid control unit prescribes parameters corresponding to settings ofsaid device which are suitable for a first type of recording media, andsaid evaluation means emits an output signal to said control unit forchanging said parameters if said signals emitted by said detection meansare not within said predetermined range.
 3. The device according toclaim 2, wherein: said evaluation means evaluates said signals emittedwith said detection means while said focus point is shifted along saidoptical axis.
 4. The device according to claim 2, wherein: said focusingmeans has a multiple-focus lens.
 5. A device for writing to or readingfrom an optical recording medium, comprising: focusing means forshifting a focus point along an optical axis; detection means fordetecting light reflected from said optical recording medium; andevaluation means for distinguishing the physical properties of saidoptical recording medium by evaluating time characteristics of a signalemitted by said detection means, wherein said time characteristics aredetermined by a combination of different signals.
 6. The deviceaccording to claim 5, wherein said different signals are a focus errorsignal and a mirror signal.
 7. The device according to claim 5, wherein:one of time acquisition means for determining a plurality of timeintervals between extreme values of said emitted signal and magnitudeacquisition means for determining the magnitude of a plurality ofextreme values of said emitted signal is present.
 8. The deviceaccording to claim 7, wherein: a sequence of one of said time intervalsdetermined and said magnitudes determined is evaluated.
 9. The deviceaccording to claim 5, wherein: said evaluation means evaluates saidsignal emitted with said detection means while said focus point isshifted along said optical axis.
 10. The device according to claim 5,wherein: said focusing means has a multiple-focus lens.
 11. A device forwriting to or reading from an optical recording medium, comprising:focusing means for shifting a focus point along an optical axis;detection means for detecting the light reflected from the opticalrecording medium; and evaluation means for distinguishing physicalproperties of said optical recording medium by evaluating timecharacteristics of a signal emitted by said detection means; wherein atleast one of relafive and absolute values of a plurality of extremevalues of said signal are compared to one another.
 12. The deviceaccording to claim 11, wherein: one of time acquisition means fordetermining a plurality of time intervals between extreme values of saidemitted signal and magnitude acquisition means for determining themagnitude of a plurality of extreme values of said emitted signal ispresent.
 13. The device according to claim 12, wherein: a sequence ofone of said time intervals determined and said magnitudes determined isevaluated.
 14. The device according to claim 11, wherein: saidevaluation means evaluates said signal emitted with said detection meanswhile said focus point is shifted along said optical axis.
 15. Thedevice according to claim 11, wherein: said focusing means has amultiple-focus lens.
 16. A device for writing to or reading from anoptical recording medium, comprising: focusing means for shifting afocus point along an optical axis; detection means for detecting thelight reflected from the optical recording medium; and evaluation meansfor distinguishing physical properties of said optical recording mediumby evaluating time characteristics of a signal emitted by said detectionmeans; wherein said focusing means has at least two beam paths which areoptically corrected differently and whose signal characteristics withrespect to time are evaluated jointly.
 17. The device according to claim16, wherein: one of time acquisition means for determining a pluralityof time intervals between extreme values of said emitted signal andmagnitude acquisition means for determining the magnitude of a pluralityof extreme values of said emitted signal is present.
 18. The deviceaccording to claim 17, wherein: a sequence of one of said time intervalsdetermined and said magnitudes determined is evaluated.
 19. The deviceaccording to claim 16, wherein: said evaluation means evaluates saidsignal emitted with said detection means while said focus point isshifted along said optical axis.
 20. The device according to claim 16,wherein: said focusing means has a multiple-focus lens.
 21. A device forwriting to or reading from an optical recording medium, comprising:focusing means for shifting a focus point along an optical axis;detection means for detecting the light reflected from the opticalrecording medium; evaluation means for distinguishing the physicalproperties of the optical recording medium by evaluating a plurality oftime related characteristics of a signal emitted by said detectionmeans; a memory device for storing signal characteristics emitted bysaid detection means, which characteristics are caused by the differenttypes of optical recording media; and a comparison device which comparesa measured signal characteristic with said stored signal characteristicsto determine which type of optical recording medium is present.
 22. Thedevice according to claim 21, wherein: said evaluation means evaluatessaid signal emitted with said detection means while said focus point isshifted along said optical axis.
 23. The device according to claim 21,wherein: said focusing means has a multiple-focus lens.
 24. A method forchanging settings for shifting a focus point of a device for writing toor reading from an optical recording medium in accordance with thephysical properties of the optical recording medium, comprising thefollowing steps: inserting said recording medium into said device;shifting of said focus point along an optical axis in accordance withpredetermined settings of said device which are matched to a first typeof recording media; detecting light reflected from said opticalrecording medium during said shifting step; generating a signal fromsaid detecting step which corresponds to said reflected light intensity;determining at least one of relative value and absolute value of aplurality of extreme values of said signal; determining time intervalsbetween said extreme values of said signal; comparing said extremevalues and relative intervals between said extreme values; determiningsettings which are suitable for physical properties of said insertedrecording medium on the basis of the comparison; and changing of saidsettings for shifting said focus point of said device to said determinedsettings.